Stockholders' Equity - Schedule of Treasury Stock (Details) - USD ($) shares in Thousands, $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Treasury Stock
Beginning balance	$ (169)
Ending balance	$ (209)
Treasury Stock
Treasury Shares
Beginning balance (in shares)	(5,571)	0
Repurchase of common stock for tax withholdings related to stock-based compensation (in shares)	(204)	(115)
Repurchase of common stock under share repurchase program (in shares)	(2,156)	(5,150)
Stock reissuances (in shares)	1,175	227
Ending balance (in shares)	(6,756)	(5,038)
Treasury Stock
Beginning balance	$ (169)	$ 0
Repurchase of common stock for tax withholdings related to stock-based compensation	(7)	(4)
Repurchase of common stock under share repurchase program	(76)	(153)
Stock reissuances	43	7
Ending balance	$ (209)	$ (150)